| Opacity protein opA54 | NMH_0784 | E6MVU6 | 1 |
| Opacity-associated protein OapB | SC1083_1821 | G4AAE8 | 1 |
| Opacity-related protein POPM1 | opr | P10170 | 1 |
| OpaR | VSAK1_04725 | A6D6A8 | 1 |
| OprD family outer membrane porin | B195_20390 | M5QDM2 | 1 |
| OprD family outer membrane porin | B195_12296 | M5QI02 | 1 |
| OprD family outer membrane porin | B195_07225 | M5QKB6 | 1 |
| OpuCA protein | opuCA | Q7AP65 | 1 |
| OpuCC protein | opuCC | Q7AP67 | 1 |
| Orn/Lys/Arg decarboxylase, major domain protein | EDWATA_00181 | D4F0F7 | 1 |
| Ornithine aminotransferase (OAT) (EC 2.6.1.13) (Ornithine--oxo-acid aminotransferase) | rocD SAOUHSC_00894 | Q2FZU6 | 1 |
| Ornithine carbamoyltransferase (OTCase) (EC 2.1.3.3) | B195_06370 | M5QXT9 | 1 |
| Ornithine carbamoyltransferase (OTCase) (EC 2.1.3.3) | argF AC1_0180 | B1R7A6 | 1 |
| Ornithine carbamoyltransferase (OTCase) (EC 2.1.3.3) | argI YPO3446 y0740 YP_0638 | Q8ZBG8 | 1 |
| Ornithine carbamoyltransferase (OTCase) (EC 2.1.3.3) | argF Rv1656 MTCY06H11.21 | P9WIT9 | 1 |
| Ornithine carbamoyltransferase, catabolic (OTCase) (EC 2.1.3.3) | arcB SPy_1544 M5005_Spy1273 | P0C0D0 | 1 |
| Ornithine cyclodeaminase | FTN_1444 | A0Q7U7 | 1 |
| Ornithine decarboxylase | speC PA4519 | Q9HVQ3 | 1 |
| Ornithine decarboxylase (EC 4.1.1.17) | speC PP_0864 | Q88PI6 | 1 |
| Orotate phosphoribosyltransferase (OPRT) (OPRTase) (EC 2.4.2.10) | pyrE PP_5291 | Q88C92 | 1 |
| Orotate phosphoribosyltransferase (OPRT) (OPRTase) (EC 2.4.2.10) | pyrE SPy_0901 M5005_Spy0704 | Q9A076 | 1 |
| Orotidine 5'-phosphate decarboxylase (EC 4.1.1.23) (OMP decarboxylase) (OMPDCase) (OMPdecase) | pyrF b1281 JW1273 | P08244 | 1 |
| Osmotically-inducible lipoprotein B | osmB b1283 JW1275 | P0ADA7 | 1 |
| Osmotically-inducible lipoprotein OsmE | PP_4855 | Q88DH0 | 1 |
| Osmotically-inducible protein OsmY (Putative periplasmic protein) | yraP S3408 SF3191 AJR25_007340 AJR26_006270 AJR27_007805 | Q83Q18 | 1 |
| Osmotically-inducible protein Y | osmY b4376 JW4338 | P0AFH8 | 1 |
| Osmotically-inducible putative lipoprotein OsmE (Activator of ntr-like gene protein) | osmE SF1487 S1604 | P0ADB3 | 1 |
| Osmotically-inducible putative lipoprotein OsmE (Activator of ntr-like gene protein) | osmE Z2769 ECs2445 | P0ADB2 | 1 |
| OsmY protein | SC1083_0780 | G4A7I4 | 1 |
| Outer membrane antigenic lipoprotein B | SC1083_0263 | G4A624 | 1 |
| Outer membrane associated protein | Fphi_0120 | B0TY99 | 1 |
| Outer membrane associated protein | OOM_1284 | I2AZV6 | 1 |
| Outer membrane associated protein | fopA1 FTT_0583 | Q5NH85 | 1 |
| Outer membrane autotransporter barrel domain protein | NMH_0192 | E6MVI6 | 1 |
| Outer membrane beta-barrel domain protein | J582_1346 | A0A010K0B1 | 1 |
| Outer membrane channel specific tolerance to colicin E1 segregation of daughter chromosomes, role in organic solvent tolerance | tolC SCH_3130 | Q57JS6 | 1 |
| Outer membrane channel TolC (Outer membrane channel protein TolC) | tolC S3280 SF3075 AJR25_005945 AJR27_002255 | A0A0H2VXZ7 | 1 |
| Outer membrane channel TolC (Outer membrane channel specific tolerance to colicin E1 segregation of daughter chromosomes) | tolC ECs3923 Z4392 | Q8XBP7 | 1 |
| Outer membrane chaperone Skp | B195_06025 | M5QK80 | 1 |
| Outer membrane cobalamin receptor protein | AB237_0541 | A0A0E1PNK2 | 1 |
| Outer membrane efflux family protein | NMH_0534 | E6MUT1 | 1 |
| Outer membrane efflux family protein | HPSD74_2063 | U4SB13 | 1 |
| Outer membrane efflux protein | MXAN_4176 | Q1D4S2 | 1 |
| Outer membrane efflux protein | FTN_1277 | A0Q7E3 | 1 |
| Outer membrane efflux protein | PP_0805 | Q88PP3 | 1 |
| Outer membrane efflux protein | NSU_4294 | G6EIX3 | 1 |
| Outer membrane efflux protein | FSU_1331 | C9RNP7 | 1 |
| Outer membrane efflux protein | FSU_2056 | C9RRI0 | 1 |
| Outer membrane efflux protein | FSU_1095 | D9S9F8 | 1 |
| Outer membrane efflux protein | FTT_1258 | Q5NFH6 | 1 |
| Outer membrane family protein | KW89_755 | A0A0K2DV57 | 1 |
| Outer membrane ferric siderophore receptor | PP_2420 | Q88K71 | 1 |
| Outer membrane ferric siderophore receptor | PP_0272 | Q88R62 | 1 |
| Outer membrane ferric siderophore receptor | PP_2193 | Q88KU6 | 1 |
| Outer membrane ferrichrome-iron receptor | PP_0350 | Q88QY4 | 1 |
| Outer membrane lipoprotein | blc FTN_0174 | A0Q4B9 | 1 |
| Outer membrane lipoprotein | nlpD ETAE_2874 | D0ZDS8 | 1 |
| Outer membrane lipoprotein | FTT_0211c | Q5NI73 | 1 |
| Outer membrane lipoprotein blc | VS_2109 | B7VH84 | 1 |
| Outer membrane lipoprotein Blc | blc PA5107 | Q9HU76 | 1 |
| Outer membrane lipoprotein Blc | blc FTT_0198 | Q5NI83 | 1 |
| Outer membrane lipoprotein Gna33 (EC 3.2.1.-) | NMBB_0038 | E3D514 | 1 |
| Outer membrane lipoprotein OprI | B195_20073 | M5QCY2 | 1 |
| Outer membrane lipoprotein pcp | SC1083_0209 | G4A5X1 | 1 |
| Outer membrane lipoprotein RcsF | rcsF b0196 JW0192 | P69411 | 1 |
| Outer membrane lipoprotein RcsF | rcsF KPN_00210 | A6T4Z9 | 1 |
| Outer membrane lipoprotein Slp family | VS_2222 | B7VI16 | 1 |
| Outer membrane lipoprotein Slp, putative | VC_1987 | Q9KQL1 | 1 |
| Outer membrane lipoprotein SlyB | slyB SF1668 S1800 | P0A907 | 1 |
| Outer membrane OpcA family protein | NMH_1358 | E6MXF3 | 1 |
| Outer membrane phospholipase A | pldA KPN_04316 | A6TGK0 | 1 |
| Outer membrane pore protein | KPN_02430 | A6TB82 | 1 |
| Outer membrane pore protein 1b (Ibc) | ompC KPN_02636 | A6TBT2 | 1 |
| Outer membrane pore protein E | phoE ompE b0241 JW0231 | P02932 | 1 |
| Outer membrane pore protein E (E,Ic,NmpAB) | phoE SSON_0283 | Q3Z596 | 1 |
| Outer membrane pore protein, receptor for ferrichrome, colicin M, and phages T1, T5 and phi80 | fhuA KPN_00165 | A6T4V4 | 1 |
| Outer membrane porin | B195_16594 | M5QGS3 | 1 |
| Outer membrane porin | B195_15022 | M5QHJ6 | 1 |
| Outer membrane porin | B195_12881 | M5QVR7 | 1 |
| Outer membrane porin | B195_01960 | M5QMV2 | 1 |
| Outer membrane porin F | KU39_120 | A0A0K2KZF4 | 1 |
| Outer membrane porin protein OmpD | ompD SCH_1572 | Q57P83 | 1 |
| Outer membrane porin protein, putative ferrisiderophore receptor | ybiL KPN_01250 | A6T7W2 | 1 |
| Outer membrane porin, OprD family protein | B195_11971 | M5QHU1 | 1 |
| Outer membrane porin, receptor for ferric enterobactin (Enterochelin) and colicins B and D | fepA STM0585 | Q8ZR40 | 1 |
| Outer membrane porin, receptor for ferric enterobactin and colicins B and D | fepA KPN_00602 | A6T631 | 1 |
| Outer membrane protease E (E protein) (EC 3.4.23.-) | pgtE prtA STM2395 | P06185 | 1 |
| Outer membrane protease IcsP (EC 3.4.23.-) | icsP sopA CP0271 | O33641 | 1 |
| Outer membrane protease OmpP (EC 3.4.23.-) | ompP ompX ECOK12F029 | P34210 | 1 |
| Outer membrane protease, receptor for phage OX2 | ompX SCH_0829 | Q57RC6 | 1 |
| Outer membrane protein | ompS2 | Q8GF10 | 1 |
| Outer membrane protein | VS_0685 | B7VKC4 | 1 |
| Outer membrane protein | VS_1393 | B7VNI0 | 1 |
| Outer membrane protein | VS_1843 | B7VPS6 | 1 |
| Outer membrane protein | VS_II0310 | B7VQS8 | 1 |
| Outer membrane protein | FTT_1747 | Q5NEA1 | 1 |
| Outer membrane protein (Omp7) | HP_0252 | O25034 | 1 |
| Outer membrane protein (Surface protein A) | nspA ERS514708_01475 | Q9RP18 | 1 |
| Outer membrane protein 18/16 | SC1083_1267 | G4A8W4 | 1 |
| Outer membrane protein 1a (IabF) (Phosphoporin PhoE) | ompF S0990 SF0926 AJR25_014815 | Q83RY4 | 1 |